Troubleshooting with a temp gun?

[barrelroll]

Twice now a temp gun has bit me in the ass leading me to the wrong diagnosis. Once I thought I had a BO temp sensor on an air compressor and I missed the room temperature cooler line. Another time I though I had a bad temp gauge on a diesel pump, turns out it was actually running hot.

What are your "rules" for using a temp gun to verify gauges/ sensors are working right with one?

I finally got a thermostat in the diesel pump last night. It turns out one of the 2 webs holding the t-stat together was broken allowing the shaft in the t-stat to go crooked and limiting how much it would open and flow, also every hose started leaking when the coolant pressure tester put a couple PSI on the system. You could see the thermostat opening/ closing temp wise with the temp gun though I had no way of knowing it was broken till I pulled the t-stat housing to look for junk in it. It now runs around 175 to 180 on the gauge and around 145 with a temp gun at the t-stat where the sender is. It was running 220+ on the gauge and around 175/180 with a temp gun in the same areas.

Any tips on trouble shooting overheating issues with a temp gun? I'm leaning towards a rough rule of thumb of a 40 degree drop between fluid temps and metal temps of the sensor with the temp gun. When I have a chance I need to make some notes on what's a normal metal temp compared to the temp on the gauge on some of the stuff I work on often.

 

[Vetech63]

I would verify that your temp gun is accurate. Have your wife put on a boiling pot of water tonight and throw her meat thermometer in it......then shoot the pot with your gun. Compare those readings. Metal absorbs the heat from the liquid flowing inside......they should be relatively close in temps.

 

[barrelroll]

I would verify that your temp gun is accurate. Have your wife put on a boiling pot of water tonight and throw her meat thermometer in it......then shoot the pot with your gun. Compare those readings. Metal absorbs the heat from the liquid flowing inside......they should be relatively close in temps.

The main one I use is a "shop tool", used by everyone, thrown in the back of a pickup, dragged underground. Looking up the reviews on the Milwaukee web site for our main shop temp gun are horrible saying it's out of calibration. I have an older Ryobi and there's a fluke running around the shop I'll have to compare the 3. I never thought about the gun being the issue, I figured it was the idiot behind the gun.

Any recommendations on a decent temp gun?

 

[Vetech63]

I have a raytech and a fluke

 

[Btad]

You need to get the gun as close as possible
The farther away the less acute it is
I learned this the hard way

If you try to use that thermometer to measure a two-inch (5-cm) area from even just a few feet (1 m) away, you're not going to get an accurate result because the thermometer will also be measuring the temperature outside the area you want to measure.

 

[Delmer]

Yes, you have to be close. I think an angle of 7:1 is typical, but use less, if you're 4" away you're measuring a 1" circle. The laser is a joke, it doesn't help in any way that I can see, it plays on role in measuring, just an aid, and a confusing one at that.

The gun has to be clean, and set on the right emissivity also. It won't work on shiny surfaces like chrome. I'd expect 40F difference reading the outside of a rubber hose compared to the internal temp, it is reading surface temp after all, and the insulating value of the hose will lead to a lower surface temp. Cast iron or painted aluminum or brass should be within a few degrees of the water temp inside. Assuming the air temp is not below zero at least.

 

[JD955SC]

These things are cheap enough you need to get your own vs relying on a beat to hell shop one. I hate using shop diagnostic tools, it’s a sure way to get yourself screwed on diagnosing.

12:1 spot ratio is the typical Temp gun. A higher ratio is a feature of more expensive guns. This means you have to be pretty close to use what most of us have on smaller components and make sure not to overshoot your intended measurement point.

Most temp guns use a dot for aiming. The more sophisticated ones will use a circle that indicates the measured area.

Most temp guns use a fixed emissivity level of .95. This means that they are most accurate for a non reflective darker material. Shooting a shiny hydraulic valve block or a radiator will vastly throw off your readings. I have used the trick of some spray paint to darken a shiny surface. https://ennologic.com/emissivity-infrared-thermometer-readings/

You are correct in that the metal does shed heat so it’s a lower temp than the fluid. Aluminum is an especially effective conductor of heat, it radiates it off quick.

For engine coolant temps I find the most accurate source is the thermostat housing which is where I try to take my performance readings and see how close the temp sensor is as it’s usually in it also.

 

[Camshawn]

In most temp guns, the sensor looks at a cone shaped area. The closer the sensor, the more accurate the reading as the area of the cone is smaller the closer the sensor is to the surface.
Black electrician tape has an emissivity of around 0.95. If you need to compare 2 surfaces of different colours or materials, put some black tape on them and that will standardize your readings. Cam

 

[barrelroll]

Thanks for all the tips. I've definitely learned some things and need to do some more reading/ learning on a couple things now.

With rotary screw compressors there's a solid 20+ degree jump from loaded to unloaded temps, most sensors are in a decently thick piece of iron. Would you expect it to heat soak to the unloaded temp/ how fast would you expect the iron to change temps?

Thinking back on it when I first started here I was doing PM's with my dirt simple 10 year old Ryobi. One of the guys was using the shop's Milwaukee and thought my gun was off, hence why I was using the shop gun.

We also have a Fluke 62 Max + with the dual lasers which is confusing though after reading the fluke picture manual it makes more sense.

 

[nowing75]

just got a flir tg267 thermal imager. Have not used it much but looks like it could come in handy.

 

[Delmer]

with coolant flowing through metal, I expect a few degrees difference in average weather. A rotary screw compressor will be a little different, as it's a mix of hot air and oil inside the pipes, right? so even the oil will be lower conductivity and heat capacity than coolant, so it won't change the temp of the metal as fast, or reach as close a temp as it would with coolant, that's my guess. The thicker iron will make the change even slower. On a thermostat housing, the temp change is very little, so response time is not much of a factor.

 

[JD955SC]

just got a flir tg267 thermal imager. Have not used it much but looks like it could come in handy.

We have one at work, I finally got our boss to buy it.

It’s good, just expect for the camera and IR image to be off a little due to two different lenses.

 

[barrelroll]

I had a chance to shoot temps on the diesel pump today with my old beater Ryobi. I was getting temps really close to the cheap analog gauge on the control panel. Previously with the Milwaukee I was getting temps 20+ degrees lower than the gauge. It was running 220+ and shutting down on the high temp switch, I could never get temps close to that with the Milwaukee. Shooting the t-stat housing did give me much closer temps to the gauge than shooting the sender.

 

[terex herder]

No need for the meat thermometer in the pot of boiling water. If atmospheric pressure is known, the boiling point of water is known and published quite accurately. The boiling point was used to calibrate thermometers and the creation of the temperature scale.

 

[Mike L]

Skip the temp gun and buy a thermal imager. Much more money but much more capability

 

[treemuncher]

I'll second a Thermal Image Camera. My Blackview BV9800 Pro is a super rugged phone with the built in TI camera. It allows for precise thermal differences to be shown in multiple colors with distinct location temps to the tenth of a degree.

It's a lot more precise than any temp gun that I've used and it's the best phone I've had. Fast, TONS of memory, fast processor and several cameras built in.

 

[Vetech63]

I'll second a Thermal Image Camera. My Blackview BV9800 Pro is a super rugged phone with the built in TI camera. It allows for precise thermal differences to be shown in multiple colors with distinct location temps to the tenth of a degree.

It's a lot more precise than any temp gun that I've used and it's the best phone I've had. Fast, TONS of memory, fast processor and several cameras built in.

Way late in my career but what would one of those set me back today?

 

[Mike L]

Snap on was about $1500 so everything else is about $89

 

[treemuncher]

Way late in my career but what would one of those set me back today?

Maybe 2 years ago it was about $400. I purchased through sunsky.com out of Hong Kong. Ordered Saturday night and was delivered Tuesday afternoon. Battery lasts me about 2 days, wife, not so much!

Takes some tricks to get it set up with Verizon but it works fine. Blackview likely has new models by now.

 

[MarshallPowerGen]

Way late in my career but what would one of those set me back today?

I use a Klein TI250 Thermal Imager pretty regularly, they only run about $300 to your door.

Looks like Klein now offers a plug into your phone kind, but last one of those I was provided (FLIR) needed to be charged every time I went to use it.